Causative agent of trichuriosis
Occurrence. Trichuris trichiura occurs in humans and monkeys. Although this parasite has a worldwide distribution, it is found most frequently, like Ascaris lumbricoides, in moist, warm areas with low hygienic standards (prevalence around 2-90%). The number of infected persons worldwide is estimated at one billion (WHO, 1998).
Parasite, life cycle, and epidemiology (Fig. 10.13). The name whipworm characterizes the form of this 3-5 cm long nematode with a very thin anterior part reminiscent of a whiplash and a thicker posterior "handle." The adult nema-todes live in the large intestine, mainly in the cecum. The females lay 200014 000 thick-shelled, yellow-brown eggs per day. The eggs are about 5055 im long and are readily identified by their lemonlike shape and hyaline polar plugs (Fig. 10.1, p. 544). An infective larva develops in the egg within a few weeks. In moist surroundings, Trichuris eggs remain viable for months or even years.
Following peroral ingestion of infective eggs, the larvae hatch in the digestive tract, migrate into the mucosa, and return to the intestinal lumen after a histotropic phase lasting about 10 days. There the adult stages develop and remain with their slender anterior ends anchored in the mucosa. The prepa-tent period is two and a half to three months, the parasite can live for several years.
A moist, warm climate and unhygienic practices favor infections, which are contracted as described for Ascaris.
Pathogenesis and clinical manifestations. The whipworms, with their thin anterior ends anchored in the mucosa, ingest blood. Mild infections are asymptomatic. More severe infections, with hundreds or several thousand whipworms, cause catarrhal or hemorrhagic inflammations of the large intestine.
Diagnosis, therapy, and control. A Trichuris infection is diagnosed by detecting eggs in stool (Fig. 10.1, p. 544). Effective drugs include albendazole, mebendazole, and oxantel. See ascariosis for appropriate prevention and control measures.
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